Hi Nora,
I won't attempt an I.D., except to say your specimen does sound too
large for N. proxima.  Divaricate sculpture consists of radial
grooves or ridges that change direction at an abrupt angle, so that
they give the impression of being "V-shaped".  Acila divaricata is a
member of Nuculidae named for that characteristic.
Getting Nucula valves rearticulated can be a problem, because of the
many very fine teeth that have to mesh precisely.  Nuculanidae are
also difficult, and Trigoniidae are probably the worst!  Their hinges
have more teeth, ridges, and furrows than anything else I have seen!
I have had the best luck with such shells by starting with the valves
almost opened wide ("butterfly style", the way some folks display
tellins).  Bring the umbos together first, without the hinge teeth
touching, then gently rotate or "rock" the valves toward each other,
keeping the umbos in contact, while very gently wiggling the valves
against each other.  Usually the teeth will mesh this way.  If you
bring the valves directly toward each other, flat surface to flat
surface, the teeth cannot mesh properly (as you have apparently
already discovered).  For small specimens, directly observing the
meshing of the teeth under the microscope can be very helpful.
Regards,
Paul M.
Rhode Island, USA